340 cases of hookworm infection, 196 cases of ascariasis and 178 cases of trichuriasis were treated with an anthelmintic, oxibendazole, 15mg/kg.d x 3d; 102, 70 and 66 cases of respective infections were treated with pyrantel 10mg/kg.d x 3d and 108, 74 and 63 cases took placebo for comparison and as control under double-blind observations. Re-examinations of the stool were performed after the treatment. Among the cases treated with oxibendazole, the egg negative conversion rates of hookworm, Ascaris and Trichuris were 70.3-80.6%, 92.5-97.8 and 67.0-71.0% respectively. The egg reduction rates of hookworm were 98.1-98.6%. The larval negative conversion rates of Ancylostoma duodenale and Necator americanus were 77.7 and 83.2% respectively. Among the cases treated with pyrantel, the egg negative conversion rates of the three above mentioned parasites were 73.5, 90.0 and 28.8% respectively. The egg reduction rate of hookworm was 98.8%. Among the cases treated with placebo, the egg negative conversion rates of the three above mentioned parasites were 6.5, 29.7 and 7.9%. No marked adverse reactions were observed by clinical and laboratory examinations.